You ''could'' share a profile. Just place the profile you wish to share in a location where you can both access it, and each set your own ''profiles.ini'' file to select it. The profile manager is one way to do this. https://support.mozilla.org/en-US/kb/using-multiple-profiles I have daily ongoing differences with my wife about my own "everything in its place and a place for everything" methods and her rather more bohemian approach. So, for my own sanity, I wouldn't choose to share a profile. A halfway house is to share just selected address books. I think the Address Book Synchronizer add-on may be of use to you. Note that it doesn't offer real-time synchronisation; the current user downloads the selected address books, changes them in the course of using Thunderbird, and when closing Thunderbird, the changed address books are uploaded back to the communal store. This won't suit you if you both use Thunderbird at the same time. https://www.ggbs.de/extensions/AddressbooksSynchronizer.html